A plurality of programs are generated which are each composed of an arrangement of basic instructions of plural types required to generate output data with respect to given input data of given types. Each of the programs is executed with a computer until a predetermined condition is satisfied, and the input data is given to the computer. Output data generated with respect to the input data when each of the programs is executed is compared with reference output data predetermined with respect to the input data, and an energy value indicative of the quality level of each of the programs is incremented or decremented such that the energy value is greater as the degree with which the generated output data and the reference output data agree with each other is higher. Each of the programs is copied or eliminated depending on the magnitude of the energy value after the execution of each of the programs by the computer is finished, and the programs are crossed and mutated with a predetermined probability. The above steps of executing, incrementing or decrementing, copying or eliminating, crossing, and mutating are repeated to generate a program for generating output data with respect to the input data with a high degree of agreement with the reference output data.